Multiple fuel firing method and apparatus



June 2, 1964 A. BRUNNER MULTIPLE FUEL FIRING METHOD AND APPARATUS 2 Sheets-Sheet 1 Filed Dec. 14, 1960 June 2, 1964 A. BRUNNER MULTIPLE FUEL FIRING METHOD AND APPARATUS Filed Dec. 14, 1960 2 Sheets-Sheet 2 n. m 6 N n 8N P WW m fl B 1 D K a M 4 234 11 1 w 1m; NJ 7% 3 I26 H79 70 60 as /25\ United States Patent Claims priority, application Switzerland Dec. 23, 1959 7 Claims. (Cl. 158-11) The present invention relates to a method and apparatus for burning at least two different fuels in a plurality of burners for each fuel and more particularly to a control method and apparatus therefor.

In Patent No. 3,049,168 to Richard Litwinoff a method is disclosed wherein, in a firing apparatus for burning a plurality of different fuels and having a plurality of burners for each fuel, the number of burners operated for each kind of fuel corresponds to the relative amounts of different fuels to be burned at a given time and wherein the total heat output of the firing apparatus is controlled by adjustment of the output of all burners which are in operation. The aforesaid adjustment is effected by adjusting, if, for example, oil and gas are the different fuels, the pressure in the supply pipes to the burners according to the total desired heat output. The number of burners operated for each of the'different fuels is not changed upon a change of the total output of the firing apparatus. 7

If one of the fuels, for example blast-furnace gas or natural gas, cannot be accumulated without great expense, the method described in the paragraph next above cannot be used economically, because upon a reduction of the total output of the firing apparatus the rate of flow of this fuel to the burners is also reduced and, if this fuel is available at a greater rate, the unused fuel would do not coincide with the amounts required by the respective burners at these times. According to the invention the number of the burners for burning the fuel which, at times, would have to be stored but cannot bestored economically and which will henceforth be called the basic fuel, is adjusted according to the quantitative availability of the basic fuel and is so adjusted that the flow rate of this fuel in a conduit common to all burners of the firing apparatus is between a predetermined upper and a predetermined lower value. For obtaining an indication of the quantitative availability of the basic fuel, the pressure in its common supply line may be measured or a small accumulator may be connected to said line and the fuel accumulation-therein may be measured.

use of fuel which, at times, is available in amounts which i t The invention relates to a multiple fuel firing apparatus 5 1 invention the burners of each unit are so constructed that taneously closing of a second valve to closing of the first valve and opening of the second valve is effected in response to changes of the quantitative availability of the basic'fuel.

If each burner unit comprises a burner for the basic 3,135,314 Patented June 2, 1964 ii ce fuel and burners for at least two different additional fuels which are selectively used, the burner switching mechanisms which are actuated in response to changes of availability of the basic fuel act on the valves for the basic fuel burners and individually act on additional mechanisms which can be preset by hand to stop fuel supply of additional fuels to the burners of the respective units except to one burner. The burner switching. mechanisms individually actuate the additional mechanisms for stopping fuel admission to the additional fuel burners to which supply of fuel is not stopped by the presetting of the additional mechanisms, upon availability of basic fuel and supply thereof to the respective burners, and for leaving open the fuel admission to the additional fuel burners which are initially not stopped, upon stoppage burners for the basic fuel.

The novel features which are considered characteristic of the invention are set forth with particularity in the appended claims. The invention itself, however, and additional objects and advantages thereof will best be understood from the following description of embodiments thereof when read in connection with the accompanying drawing, wherein:

FIG. 1 is a diagrammatic part sectional illustration of one of four identical rows of burner units and ofa mechanism for controlling the operation of the burner units.

FIG. 2 illustrates two parts of the contact surface of a drum switch forming part of the control mechanism shown in FIG. 1.

FIG. 3 is a diagrammatic part sectional illustration of a part of a modified system according to the invention.

The right side of FIG. 1 shows one of four rows of burner units of a furnace of a steam generator, not shown. It is assumed that the heat-producing capacity of the burner unit 1 is one fifth of the capacity of the burner unit 2 and one twentyfifth of the heat-producing capacity of each of the units 3 and 4. The relative capacities of the burner units forming the three rows, not shown, is the same as the relative capacities of the illustrated burner units. There are altogether sixteen burner units forming four groups of units, the burner units of each group being identical and having the same heat output capacity, only one unit of each group being shown in FIG. 1.

Each burner unit is connected to an air distributing conduit 5, a fuel oil distributing conduit 6 and a fuel gas distributing conduit 7. The pressure in these conduits is maintained by conventional means preferably according to the load on the system, for example, as shown in Patent No. 3,049,168. A control for the pressure in the distributing conduit 7 which receives fuel gas from a supply conduit 30, is diagrammatically indicated. The

of the gas-accumulating capacity of the conduit 30 is small and a valve 50 is interposed in this conduit which valve is controlled by a regulator 51 in response to gas pressure in the conduit 30 downstream of the valve 50 which pressure is measured by a conventional device 52 and compared in the device 51 with a set point value signal which is introduced through a signal conduit 53 and corresponds to the total heat output demanded from the firing apparatus.

Valves 10 and 11 are interposed in each burner unit between the distributing conduits 7 and 6 for the fuel gas and the fuel oil, respectively, and gas burners 8 and oil burners 9, respectively. The valves 10 and 11 of each unit are connected to different arms of a lever 12 which is actuated by a solenoid 15 so that, if one valve is open, the other valve is closed. Energizing of the solenoids 15 is controlled by a contact roller 20 whose angular position is controlled in response to the pressure in the conduit 30 which acts on a diaphragm 32. The latter actuates a reversing switch 33 whenever the pressure in the conduit 30 is above or below a predetermined value. These values are relatively far apart due to the gas-accumulating capacity of the conduit 30 and the inertia of the diaphragm device 32 and the switch 33. Asmall storage vessel 31 may be interposed in the conduit 30 for increasing the gas storage capacity of the conduit. The arrangement permits a predetermined variation of the pressure in the conduit 30. e

Whenever the switch 33 reaches an extreme position a reversible motor 34 is rotated in one of two opposite directions, whereas the motor is stopped as long as the switch is between its extreme positions. The motor 34 drives the contact roller via a reducing gear 35. Seventeen wipers 36 are in engagement with the roller 20; each one of sixteen of the wipers controls flow of current through one of the solenoids 15. FIG. 2 shows the development of two portions of the surface of the roller 20 and the arrangement of the contact elements thereon which elements are represented by shaded areas.- All contact elements are electrically connected. The wipers 36 are vertical to the plane of the drawing and are indicated diagrammatically by arrows. The contact elements shown in FIG. 2 move to the right upon an increase of the pressure in line 30 corresponding to an increase of the availability of the basic fuel. They move to the left upon a decrease of the availability of the basic fuel. The numbered dotted lines in FIG. 2 indicate consecutive positions of the contact elements of the switch roller 20 when moving to the right. The numbers also indicate the total basic fuel burning capacity of the burner units which are in operation at the indicated switch positions. In the position .0 none of the solenoids 15 is energized. In the position 1 one of the solenoids 15 of the top row of the burner units 1 is energized and the corresponding burner unit burns basic fuel only; in the position 2 the solenoids of two burner units 1 are energized, and so on. In the position 5 all solenoids of the four burner units 1 forming the top row are deenergized so that they burn additional fuel only and the solenoid of one burner unit 2 is energized so that this burner unit burns basic fuel. Continued movement of the contact surface to the right causes consecutive energization of the solenoids 15 of the burner units 1. This goes on until all burner units 1 and 2 are set for burning basic fuel. Since each burner unit 2 burns five times as much basic fuel as one burner unit 1 the total fuel burning capacity corresponds now to that of twenty-four burner units 1. Further travel of the contacts to the right in FIG. 2 deenergizes the solenoids 15 of all burner units 1 and of all burner units 2 and energizes the solenoid 15 of one burner unit 3 whose capacity is twenty-five times the capacity of a burner unit 1. By moving the contacts farther to the right the basic fuel burners of the units 1 are sequentially started and after the basic fuel burners of all four units 1 are in operation in addition to the basic fuel burner of one unit 3 the basic fuel burner of one unit 2 is started and the gas burners of the units 1 are stopped whereby the total basic fuel burning capacity is increased from twenty-nine unit is energized so that the total fuel burning capacity corresponds to that of one-hundred-and-twenty-five units 1. If more basic fuel is available the contacts are still more moved to the right and the basic fuel burner of one unit 1 is started so that the total capacity increases to that of one-hundred-twenty-six units 1. This situation is illustrated in FIG. 1 wherein one basic fuel burner of the units 1, the basic fuel burners of the four units 3 and the basic fuel burner of one unit 4 are in operation.

If the heat-producing capacities of the burner units are stepped in the relation 1:5 :25, the contact roller has 225 contact steps. Advance from one step to the next step eifects a change of the total heat output produced by one of the different fuels by of the total possible heat production by this fuel in the firing apparatus. If the heat-producing capacity of the units 4 is made greater than that of the unit 3, the heat output interval between two contact steps can be reduced from to km. The interval can also be reduced by increasing the number of units per row of burner units. Usually the described arrangement of four burner units in each of four rows and the stated relative heat output capacities of the rows are sufficient.

In order to prevent going out of the fire when a burner unit is switched from one kind of fuel to another fuel, a pilot burner may be provided which is always supplied with the same type of fuel. FIG. 1 shows a pilot burner 40 in combination with the unit 4.

The apparatus shown in FIGS. 1 and 2 operates as follows:

It is assumed that the entire apparatus is in normal operation whereby the individual burner units are so supplied with fuel gas and fuel oil that all available gas, which is the basic fuel, is consumed. If now the load on the apparatus, i.e. the demanded total heat output, is reduced, the output of all burners which are in operation is'reduced as described and shown in Patent No. 3,049,168. In the system shown in FIG. 1 the set point signal arriving through the conduit 53 actuates the device 51 in a closing sense of the valve 50, upon a load reduction. If fuel gas continues to arrive through conduit 30 at the previous rate, the pressure in the conduit 30 rises and, if it rises above a predetermined value, the diaphragm 32 actuates the switch 33 and the motor 34 is started and drives the contact roller 20 in a direction effecting change of burner units from. firing oil to firing gas and increasing gas consumption. This goes on until the gas pressure in the conduit 30 is sufficiently reduced to return the die phragm 32 and the switch 33 to neutral position whereby the motor 34 is stopped. Now the firing apparatus is once more in equilibrium position. At an increased heat demand the pressure in the conduit 30 falls and burner units which have been fired with gas are switched to firing oil by rotation of the roller 20 in the opposite direction.

FIG. 3 corresponds to the right side of FIG. 1 and diagrammatically illustrates a firing apparatus in which powdered coal is burned in addition to oil and gas. Only the control mechanism for the burner unit 4 is illustrated, the mechanisms for the burner units 1, 2 and 3 being identical with that of the burner unit 4. Parts which are identical with parts shown in FIG. 1 are designated by like numerals. Each burner unit comprises a burner 60 for powdered coalin addition to a burner 9 for fuel oil and a burner 8 for fuel gas. The powdered coal burners 60 are connected to a distributing duct 61 which receives powdered coal from a supply conduit 62. Each of the conduits leading from the distributing duct 61 to a burner 60 is connected at 63 to a returnconduit 64 which terminates in a collecting duct 65. The latter returns fuel which is not used in the burners 60 to a separator 66 wherein the powdered coal is separated from the conveying air and drops through a funnel 68 into a hopper 69. The air leaves the separator 66 through an outlet 67.

At each of the locations 63 a flap'70 is provided for controlling the flow of powdered coal into the conduits 64. Each flap 76 is operatively connected by means 'of a linkage 71 to one arm of a two-arm lever 72. The other arm of the lever 72 is operatively connected to the fuel admission valve 11 of the oil burner 9 through a linkage 73. The lever 72 can be swung around its fulcrum 77 by means of a rod 74 which may be moved by hand. Depending on the position of the lever 72 fuel supply is permitted either to the powdered coal burner 60 or to the oil burner 9. Which of the additional fuels, powdered coal or oil, is used in addition to the basic fuel which is burned in the gas burner 9 depends on the availability of the fuels and their cost.

The mechanism 71 to 74 is connected "to the mechanism 12, 15 by means of a rod 75 which is connected to one arm of the lever 12, the rod 75 being longitudinally guided in a bearing 76 and having its free end connected to the fulcrum 77. of the lever 72. The lever 12 can be swung counter-clockwise against the action of a spring 16 by means of a solenoid 15. Depending on the setting of the additional mechanism171 to 73 by means of the rod 74, the individual burner units can be operated either by gas which is the basic fuel, or by one of two additional fuels, namely, oil or powdered coal. Since the selection of the additional fuel depends on economic considerations and resetting of the mechanism 71 to 74 is not frequently required, automatic control of the additional mechanism is generally not needed and manual control is sufficient.

I claim:

1. A method of controlling a firing apparatus at variable output, the apparatus having a plurality of burner units, each unit comprising a burner for a basic fuel which is available at variable amounts and must be used up at rates corresponding to said amounts, and a burner for at least one additional fuel, the method comprising the steps:

of operating basic fuel burners of predetermined burner units and simultaneously stopping the additional fuel burners of said predetermined burner units, for burning basic fuel at a rate substantially corresponding to the amount of basic fuel which is available,

of simultaneously operating the burners for the additional fuel of the burner units Whose basic fuel burners are not in operation for producing a total heat output substantially corresponding to the desired heat output of the firing apparatus, and

of increasing the heat output of all burners which are in operation upon an increase of the total heat demand and decreasing the heat output of all burners which are in operation upon a decrease of the total heat demand.

2. A method as defined in claim 1 wherein the basic fuel burners of predetermined burner units are consecutively started upon an increase of the amount of available basic fuel and are consecutively stopped upon a decrease of the amount of available basic fuel.

3. A method of controlling a firing apparatus at variable output, the apparatus having a plurality of burner units, each unit comprising a burner for a basic fuel which is available at variable amounts and must be used up at rates corresponding to said amounts, and a burner for at least one additionl fuel, the method comprising the steps:

of operating a number of the basic fuel burners at a time whose total fuel burning capacity corresponds to the amount of basic fuel available at that time,

of simultaneously stopping operation of the. additional fuel burners of the burner units whose basic fuel burners are operated,

of simultaneously operating the burners for the additional fuel of the burner units whose basic fuel burners are not in operation for producing a total heat output substantially corresponding to the desired heat output of the firing apparatus, and

of increasing the heat output of all burners which are in operation upon an increase of the total heat demand and decreasing the heat output of all burners which are in operation upon a decrease of the total heat demand.

4. A method of controlling a combustion apparatus having a plurality of burner units, each unit comprising a burner for a gaseous basic fuel which is available at variable amounts and must be used up at rates corresponding to the amounts the basic fuel is available, and a burner for at least one additional fuel, said basic fuel being supplied to said basic fuel burners from conduit means wherein the pressure corresponds to the amount of basic fuel which is available at a time, the method comprising:

measuring the pressure in said conduit means,

- selecting, in response to the measured pressure, basic fuel burners whose total fuel burning capacity corresponds to the amount of basic fuel available in said conduit means and operating the selected basic fuel burners for burning basic fuel at a rate substantially corresponding to the amount of basic fuel available,

simultaneously stopping operation of the additional fuel burners of the units whose basic fuel burners are in operation,

simultaneously operating the burners for the additional fuel of the burner units Whose basic fuel burners are not in operation for producing a total heat output substantially corresponding to the desired heat output of the firing apparatus, and

increasing the heat output of all burners which are in operation upon an increase of the total heat demand and decreasing the heat output of all burners which are in operation upon a decrease of the total heat demand.

5. A combustion apparatus for firing a basic fuel which is available in variable amounts and must be consumed at rates corresponding to the amounts at which the basic fuel is available, and for firing at least one different kind of fuel, comprising:

a plurality of burner units, each unit comprising a burner for each kind of fuel,

an apparatus connected to the burners of each unit for admitting fuel to one selected burner at a time of the respective unit while stopping fuel admission to the other burner of the unit,

separate distributing means for each kind of fuel connected to said units,

a supply conduit for the basic fuel connected to the distributing means for the basic fuel, and

control means connected to said supply conduit and responsive to changes of the amounts at which the basic fuel is available in said supply conduit and operatively connected to said apparatus for stopping admission of basic fuel to a number of burners for the basic fuel upon a reduction of the amount of available basic fuel and simultaneously admitting fuel to a corresponding number of the burners for the other fuel and for stopping fuel admission to a number of the burners for the other fuel upon an increase of the amount of available basic fuel and simultaneously admitting basic fuel to a corresponding number of the burners for the basic fuel,

the number of burners to which fuel admission is stopped and to which fuel is admitted corresponding to the extent of the change of the amount of available basic fuel.

6. A combustion apparatus as defined in claim 5 wherein said units have different fuel burning capacities and the relation between said fuel burning capacities is fixed.

7. A combustion apparatus as defined in claim 5 where in each of said units comprises a burner for the basic fuel and an additional burner for each of at least two additional diiferent kinds of fuel, said apparatus being connected to the burners for the basic fuel for stopping basic fuel admission to a number of the burners for the basic fuel upon a decrease of the amount of available basic fuel and admitting fuel to a number of burners for the basic fuel upon an increase of the amount of basic fuel, the numbers of the burners to which basic fuel admission is stopped or basic fuel is admitted depending on the extent of the change of the amount of available basic fuel, additional apparatus being individually operatively connected to said additional burners of each of said units and including setting means for setting said additional apparatus to stop fuel admission to all but one of said additional burners of the individual units, said additional apparatus being individually operatively connected to said first apparatus for stopping fuel admission to said additional burners Whereto fuel admission is not stopped by said additional apparatus upon admission of fuel to the burners for the basic fuel of the respective units.

References Cited in the file of this patent UNITED STATES PATENTS 1,512,132 Pfahl Oct. 21, 1924 9 OTHER REFERENCES Journal of the Iron and Steel Institute, page 551,

August 1947. 

5. A COMBUSTION APPARATUS FOR FIRING A BASIC FUEL WHICH IS AVAILABLE IN VARIABLE AMOUNTS AND MUST BE CONSUMED AT RATES CORRESPONDING TO THE AMOUNTS AT WHICH THE BASIC FUEL IS AVAILABLE, AND FOR FIRING AT LEAST ONE DIFFERENT KIND OF FUEL, COMPRISING: A PLURALITY OF BURNER UNITS, EACH UNIT COMPRISING A BURNER FOR EACH KIND OF FUEL, AN APPARATUS CONNECTED TO THE BURNERS OF EACH UNIT FOR ADMITTING FUEL TO ONE SELECTED BURNER AT A TIME OF THE RESPECTIVE UNIT WHILE STOPPING FUEL ADMISSION TO THE OTHER BURNER OF THE UNIT, SEPARATE DISTRIBUTING MEANS FOR EACH KIND OF FUEL CONNECTED TO SAID UNITS, A SUPPLY CONDUIT FOR THE BASIC FUEL CONNECTED TO THE DISTRIBUTING MEANS FOR THE BASIC FUEL, AND 